Hey Jag,
I don't know the answer to your question, but I was recently looking for rings myself and I could only find them for like $160 (OEM). I guess the '77 and '78 are odd years. I decided to just get the 836cc kit from CycleX since it comes with rings. Cost $399. Not sure if you were thinking about the same, but something to consider.
Oh, and one other thing. If I had the chance to do it over, I probably would have had the shop weld all of the flanges as you can see the 1 and 4 flanges even with the carbs on. So I have a weld bead on the 1 and a hex on the four. I guess it is irrelevant if your buggered flange is on the 2 or 3. Something to think about.